Method for salvaging and resintering cemented carbides



Patented Jan. 24, 1933 STATES tries STANLEY 1P. BILLINGS, OF PITTSFIELD,MASSACHUSETTS, ASSIGNOR T GENERAL ELECTRIC COMPANY, A CORPORATION OF NEWYORK METHOD FOR SALVAGING AND RESINTERING CEMENTED CARBIDES No Drawing.

The present invention relates to cemented carbides of the characterdisclosed in Schroter Reissue Patent No. 17 ,62& and more particularlyto a method for salvaging cemented carbide tool bits which have beenbroken or otherwise injured so that their usefulness is im aired ordestroyed.

(gemented carbides are largely employed 1n the form of tools such asturning tools, cut-. ting, forming,. bending dies, etc., which aregenerally copper brazed to supporting steel shanks; These tools areusually subject to very severe operating conditions and since they arequite brittle they sometimes crack or break. Under such circumstances ithas heretofore been customary to scrap the tools. Since cemented carbideis used extensively and is costly the loss from scrap materialconstitutes an important item.

I have found that scrap of this material may be salvaged by resinteringthe broken pieces under pressure. The scrap material may be broken.either into larger or small pieces and then pressed in a refractorymold. It is not necessary to break up the cemented carbide material intoa fine powder or even into very small pieces since large pieces may beresintered under pressure with satisfactory results.

Ordinarily, cemented tungsten carbide contains about 3 to of a binder orcementing material, for example cobalt. The hardness of such materialmay vary from about 85-89 on the RockwellA scale. \Vhen different gradesof cemented tungsten carbide containing varying amounts of cementingmaterial are resintered under pressure the hardness of the resinteredmaterial is usually increased to about 91 or 93 on the Rockwell A scale.

The material produced from the broken pieces of cemented carbide istough and may be pressed into relatively intricate shapes so that prelimnary grinding 1s unnecessary.

In carrying out my invention I employ a bon plungers as disclosed inGilson Patent No. 1,756,857. Broken pieces of cemented carbide areplaced in the mold between the plungers and a relatively small pressureapplied thereto while the cemented carbide is having oppositely disposedcar-' Application filed October 2, 1931. Serial No. 566,592.

heated up to its sintering temperature. The latter temperature is above1000 C. and usually from about 1350 to 1425 C. I have found that eitherno pressure or up to about 200 pounds per square inch is sufficient.Heat may be applied to the pressed material either through the plunger-sor if desired at right angles to the direction of pressure as disclosedGilson Patent No. 1,671,953. A transformer supplying 10,000 amperes atabout 10 volts will furnish a current sufficient to heat the pressedmaterial in small sections to its sintering temperature in 5 or 6.minutes.

Large sections require more current or more time. When the abovetemperature is reached I prefer to increase the pressure to about2000pounds per square inch and to maintain the latter pressure from about 2to 4 minutes depending upon the size of the part to-be fabricated.

If the cemented carbide which is being salvaged consists of tungstencarbide and cobalt, I may add a small quantity of powdered materialconsisting largely of tungsten carbide but containing an appreciableamount, for example from about 3 to 2.0% cobalt. The addition of suchpowdered material is not essential however and may be omitted ifdesired.

Before pressing and resintering the cemented carbide I prefer to removeall foreign material such as scale, grease, oil and the like. The sizeof the particles which are to be resintered appears to be immaterial.They may be of any size which will clear the mold opening. Large piecesweighing one. pound or more may be pressed and sintered as easily assmall pieces weighing one-half gramor less. The heated material infractured form becomes plastic at its sintering temperature. Thisassists in forming relatively long pieces of material into anydesiredshapc so that preliminary grinding is unnecessary.

Ordinarily. long pieces of cemented carbide cannot be fabricated frompowdered materials as the powdered material binds against the side ofthe mold and the pressure is therefore not distributed evenly throughoutthe entire body of powdered material. This is not the case however whenpieces of and the sections joined or welded together by my resinteringmethod.

Furthermore, cemented carbide parts that have become worn or broken inuse may be restored to original shape and dimension by the resinteringmethod. F or example, a

worn out sand blast nozzle may be restored by placing it in arefractorymold which has dimension and shape of the original nozzle and by addinga portion of powdered or fractured material equal to the Wear loss, thenozzle'may be restored to original dimension and shape. In case it isdesired to change the shape or dimension of sintered cemented carbideparts this may be done by the resintering method i. e. a cube may bechanged to a sphere or vice versa, or sections made for a specific usemay be changed to an entirely different form. During the resinteringoperation holes or pro1ections of any desired shape including externaland internal, straight and tapered screw threads, and definite formssuch as cutter teeth and the like may be cast from the broken carbidematerials.

By the expression large pieces as employed in the claims, I mean toexclude powdered or finely divided materials. For example, as indicatedabove large pieces weigh ing one-half gram as well as pieces weighingone pound or more may be formed or welded together into a singlefinished product.

What I claimas new and desire to secure by Letters Patent of the UnitedStates, is:

v 1. The method of salvaging a sintered hard metal compositionconsisting mainly of a refractory carbide which comprises heating largepieces of said composition in a mold at a temperature above 1000 C.while pressure is simultaneously applied thereto.,

2. The method of salvaging cemented carbide material which comprisesplacing said. material in a mold, adding to said mold a powdered mixturehaving approximately the same composition as the material in said moldand applying pressure to the material in the mold while it is heated toa temperature above 1000 C.

3. The method of salvaging a worn or broken cemented carbide structurewhich placing said material in a mold having substantially the samedimensions and shape as the original cemented carbide material,addneeaeea ing to said mold a portion of material having substantiallythe same composition as said cemented carbide material, and applyingpressure to the material in said mold, while itis heated to atemperature above 1000 C,

,5. The method of salvaging cemented carbide material which comprisesplacing large pieces of said material in a mold, applying a relativelylow pressure to said material while it is heated to its sinteringtemperature and then applyinga higher pressure and maintaining saidpressure for several minutes.

6. The method of salvaging cemented carbide which comprises cleaninglarge pieces of cemented carbide, placing the piece'sin a mold, applyinga relatively low pressure thereto while the material is heated up to atemperature of about 1400 C. and then applying higher pressure andmaintaining said pressure for several minutes. I In witness whereof, Ihave hereunto set my hand.

STANLEY P. BILLINGS,

